How bright colors help these poison tree frogs hide from predators

Jun 13, 2018

By Michael AllenJun. 13, 2018 , 11:50 AM

The striking bright blues, yellows, and oranges of poison dart frogs are a classic example of warning coloration, sending a message to predators to stay away. But somewhat counterintuitively, these conspicuous colors may be helping the frogs hide in plain sight, according to a new study.

The dyeing poison frog (Dendrobates tinctorius) lives on the forest floor in the lowland tropical rainforests of South America’s Guiana Shield, an ancient geological formation underlying the northeastern coast and parts of Venezuela and Brazil. The frogs are blue-black with a bright yellow ring around their head and back, which may be broken or joined to form a figure eight. Like a fingerprint, the pattern is unique to each frog.

Predators generally learn that such brightly colored frogs are toxic and avoid them. But this doesn’t always work. Naïve predators ignore the warning, whereas some birds and snakes seem to be able to eat poisonous frogs with few ill effects.

So researchers wondered whether poison dart frogs have another way of protecting themselves—camouflage. To find out, they first tested computational models of predator vision on images of the frogs. Their results suggested that although the amphibians are obvious at close range, their colors and patterns merge into the rainforest background as viewing distance increases.

To test those results, the scientists placed model frogs on different backgrounds in a French Guianan rainforest to see how wild predators reacted. Predators attacked frog models more often when they were placed atop an image of plain soil or a colored paper square, but less often when they were on the actual rainforest floor.

And humans seem to fall for the trick, too: People who saw images of frogs in the rainforest took longer to spot the real frogs at a distance than a frog that had been altered so that it didn’t have the same colors and patterns. Together, this suggests that although dyeing poison frogs are highly visible at close range, from far away their colors blend together for the perfect rainforest camouflage, the researchers report this month in the Proceedings of the National Academy of Sciences. The researchers speculate that the frog’s pattern is made up of a specific ratio and distribution of colors to give it the best of both worlds.